/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

package io.netty.buffer;

import io.netty.util.internal.LongCounter;
import io.netty.util.internal.PlatformDependent;
import io.netty.util.internal.StringUtil;

import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;

import static java.lang.Math.max;

abstract class PoolArena<T> implements PoolArenaMetric
{
    static final boolean HAS_UNSAFE = PlatformDependent.hasUnsafe();

    enum SizeClass {
        Tiny, Small, Normal
    }

    static final int numTinySubpagePools = 512 >>> 4;

    final PooledByteBufAllocator parent;

    private final int maxOrder;

    final int pageSize;

    final int pageShifts;

    final int chunkSize;

    final int subpageOverflowMask;

    final int numSmallSubpagePools;

    final int directMemoryCacheAlignment;

    final int directMemoryCacheAlignmentMask;

    private final PoolSubpage<T>[] tinySubpagePools;

    private final PoolSubpage<T>[] smallSubpagePools;

    private final PoolChunkList<T> q050;

    private final PoolChunkList<T> q025;

    private final PoolChunkList<T> q000;

    private final PoolChunkList<T> qInit;

    private final PoolChunkList<T> q075;

    private final PoolChunkList<T> q100;

    private final List<PoolChunkListMetric> chunkListMetrics;

    // Metrics for allocations and deallocations
    private long allocationsNormal;

    // We need to use the LongCounter here as this is not guarded via
    // synchronized block.
    private final LongCounter allocationsTiny = PlatformDependent
            .newLongCounter();

    private final LongCounter allocationsSmall = PlatformDependent
            .newLongCounter();

    private final LongCounter allocationsHuge = PlatformDependent
            .newLongCounter();

    private final LongCounter activeBytesHuge = PlatformDependent
            .newLongCounter();

    private long deallocationsTiny;

    private long deallocationsSmall;

    private long deallocationsNormal;

    // We need to use the LongCounter here as this is not guarded via
    // synchronized block.
    private final LongCounter deallocationsHuge = PlatformDependent
            .newLongCounter();

    // Number of thread caches backed by this arena.
    final AtomicInteger numThreadCaches = new AtomicInteger();

    // TODO: Test if adding padding helps under contention
    // private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;

    protected PoolArena(PooledByteBufAllocator parent, int pageSize,
            int maxOrder, int pageShifts, int chunkSize, int cacheAlignment)
    {
        this.parent = parent;
        this.pageSize = pageSize;
        this.maxOrder = maxOrder;
        this.pageShifts = pageShifts;
        this.chunkSize = chunkSize;
        directMemoryCacheAlignment = cacheAlignment;
        directMemoryCacheAlignmentMask = cacheAlignment - 1;
        subpageOverflowMask = ~(pageSize - 1);
        tinySubpagePools = newSubpagePoolArray(numTinySubpagePools);
        for (int i = 0; i < tinySubpagePools.length; i++)
        {
            tinySubpagePools[i] = newSubpagePoolHead(pageSize);
        }

        numSmallSubpagePools = pageShifts - 9;
        smallSubpagePools = newSubpagePoolArray(numSmallSubpagePools);
        for (int i = 0; i < smallSubpagePools.length; i++)
        {
            smallSubpagePools[i] = newSubpagePoolHead(pageSize);
        }

        q100 = new PoolChunkList<T>(this, null, 100, Integer.MAX_VALUE,
                chunkSize);
        q075 = new PoolChunkList<T>(this, q100, 75, 100, chunkSize);
        q050 = new PoolChunkList<T>(this, q075, 50, 100, chunkSize);
        q025 = new PoolChunkList<T>(this, q050, 25, 75, chunkSize);
        q000 = new PoolChunkList<T>(this, q025, 1, 50, chunkSize);
        qInit = new PoolChunkList<T>(this, q000, Integer.MIN_VALUE, 25,
                chunkSize);

        q100.prevList(q075);
        q075.prevList(q050);
        q050.prevList(q025);
        q025.prevList(q000);
        q000.prevList(null);
        qInit.prevList(qInit);

        List<PoolChunkListMetric> metrics = new ArrayList<PoolChunkListMetric>(
                6);
        metrics.add(qInit);
        metrics.add(q000);
        metrics.add(q025);
        metrics.add(q050);
        metrics.add(q075);
        metrics.add(q100);
        chunkListMetrics = Collections.unmodifiableList(metrics);
    }

    private PoolSubpage<T> newSubpagePoolHead(int pageSize)
    {
        PoolSubpage<T> head = new PoolSubpage<T>(pageSize);
        head.prev = head;
        head.next = head;
        return head;
    }

    @SuppressWarnings("unchecked")
    private PoolSubpage<T>[] newSubpagePoolArray(int size)
    {
        return new PoolSubpage[size];
    }

    abstract boolean isDirect();

    PooledByteBuf<T> allocate(PoolThreadCache cache, int reqCapacity,
            int maxCapacity)
    {
        PooledByteBuf<T> buf = newByteBuf(maxCapacity);
        allocate(cache, buf, reqCapacity);
        return buf;
    }

    static int tinyIdx(int normCapacity)
    {
        return normCapacity >>> 4;
    }

    static int smallIdx(int normCapacity)
    {
        int tableIdx = 0;
        int i = normCapacity >>> 10;
        while (i != 0)
        {
            i >>>= 1;
            tableIdx++;
        }
        return tableIdx;
    }

    // capacity < pageSize
    boolean isTinyOrSmall(int normCapacity)
    {
        return (normCapacity & subpageOverflowMask) == 0;
    }

    // normCapacity < 512
    static boolean isTiny(int normCapacity)
    {
        return (normCapacity & 0xFFFFFE00) == 0;
    }

    private void allocate(PoolThreadCache cache, PooledByteBuf<T> buf,
            final int reqCapacity)
    {
        final int normCapacity = normalizeCapacity(reqCapacity);
        if (isTinyOrSmall(normCapacity))
        { // capacity < pageSize
            int tableIdx;
            PoolSubpage<T>[] table;
            boolean tiny = isTiny(normCapacity);
            if (tiny)
            { // < 512
                if (cache.allocateTiny(this, buf, reqCapacity, normCapacity))
                {
                    // was able to allocate out of the cache so move on
                    return;
                }
                tableIdx = tinyIdx(normCapacity);
                table = tinySubpagePools;
            }
            else
            {
                if (cache.allocateSmall(this, buf, reqCapacity, normCapacity))
                {
                    // was able to allocate out of the cache so move on
                    return;
                }
                tableIdx = smallIdx(normCapacity);
                table = smallSubpagePools;
            }

            final PoolSubpage<T> head = table[tableIdx];

            /**
             * Synchronize on the head. This is needed as
             * {@link PoolChunk#allocateSubpage(int)} and
             * {@link PoolChunk#free(long)} may modify the doubly linked list as
             * well.
             */
            synchronized (head)
            {
                final PoolSubpage<T> s = head.next;
                if (s != head)
                {
                    assert s.doNotDestroy && s.elemSize == normCapacity;
                    long handle = s.allocate();
                    assert handle >= 0;
                    s.chunk.initBufWithSubpage(buf, handle, reqCapacity);
                    incTinySmallAllocation(tiny);
                    return;
                }
            }
            synchronized (this)
            {
                allocateNormal(buf, reqCapacity, normCapacity);
            }

            incTinySmallAllocation(tiny);
            return;
        }
        if (normCapacity <= chunkSize)
        {
            if (cache.allocateNormal(this, buf, reqCapacity, normCapacity))
            {
                // was able to allocate out of the cache so move on
                return;
            }
            synchronized (this)
            {
                allocateNormal(buf, reqCapacity, normCapacity);
                ++allocationsNormal;
            }
        }
        else
        {
            // Huge allocations are never served via the cache so just call
            // allocateHuge
            allocateHuge(buf, reqCapacity);
        }
    }

    // Method must be called insided synchronized(this) { ... } block
    private void allocateNormal(PooledByteBuf<T> buf, int reqCapacity,
            int normCapacity)
    {
        if (q050.allocate(buf, reqCapacity, normCapacity)
                || q025.allocate(buf, reqCapacity, normCapacity)
                || q000.allocate(buf, reqCapacity, normCapacity)
                || qInit.allocate(buf, reqCapacity, normCapacity)
                || q075.allocate(buf, reqCapacity, normCapacity))
        {
            return;
        }

        // Add a new chunk.
        PoolChunk<T> c = newChunk(pageSize, maxOrder, pageShifts, chunkSize);
        long handle = c.allocate(normCapacity);
        assert handle > 0;
        c.initBuf(buf, handle, reqCapacity);
        qInit.add(c);
    }

    private void incTinySmallAllocation(boolean tiny)
    {
        if (tiny)
        {
            allocationsTiny.increment();
        }
        else
        {
            allocationsSmall.increment();
        }
    }

    private void allocateHuge(PooledByteBuf<T> buf, int reqCapacity)
    {
        PoolChunk<T> chunk = newUnpooledChunk(reqCapacity);
        activeBytesHuge.add(chunk.chunkSize());
        buf.initUnpooled(chunk, reqCapacity);
        allocationsHuge.increment();
    }

    void free(PoolChunk<T> chunk, long handle, int normCapacity,
            PoolThreadCache cache)
    {
        if (chunk.unpooled)
        {
            int size = chunk.chunkSize();
            destroyChunk(chunk);
            activeBytesHuge.add(-size);
            deallocationsHuge.increment();
        }
        else
        {
            SizeClass sizeClass = sizeClass(normCapacity);
            if (cache != null
                    && cache.add(this, chunk, handle, normCapacity, sizeClass))
            {
                // cached so not free it.
                return;
            }

            freeChunk(chunk, handle, sizeClass);
        }
    }

    private SizeClass sizeClass(int normCapacity)
    {
        if (!isTinyOrSmall(normCapacity))
        {
            return SizeClass.Normal;
        }
        return isTiny(normCapacity) ? SizeClass.Tiny : SizeClass.Small;
    }

    void freeChunk(PoolChunk<T> chunk, long handle, SizeClass sizeClass)
    {
        final boolean destroyChunk;
        synchronized (this)
        {
            switch (sizeClass)
            {
                case Normal:
                    ++deallocationsNormal;
                    break;
                case Small:
                    ++deallocationsSmall;
                    break;
                case Tiny:
                    ++deallocationsTiny;
                    break;
                default:
                    throw new Error();
            }
            destroyChunk = !chunk.parent.free(chunk, handle);
        }
        if (destroyChunk)
        {
            // destroyChunk not need to be called while holding the synchronized
            // lock.
            destroyChunk(chunk);
        }
    }

    PoolSubpage<T> findSubpagePoolHead(int elemSize)
    {
        int tableIdx;
        PoolSubpage<T>[] table;
        if (isTiny(elemSize))
        { // < 512
            tableIdx = elemSize >>> 4;
            table = tinySubpagePools;
        }
        else
        {
            tableIdx = 0;
            elemSize >>>= 10;
            while (elemSize != 0)
            {
                elemSize >>>= 1;
                tableIdx++;
            }
            table = smallSubpagePools;
        }

        return table[tableIdx];
    }

    int normalizeCapacity(int reqCapacity)
    {
        if (reqCapacity < 0)
        {
            throw new IllegalArgumentException(
                    "capacity: " + reqCapacity + " (expected: 0+)");
        }

        if (reqCapacity >= chunkSize)
        {
            return directMemoryCacheAlignment == 0 ? reqCapacity
                    : alignCapacity(reqCapacity);
        }

        if (!isTiny(reqCapacity))
        { // >= 512
            // Doubled

            int normalizedCapacity = reqCapacity;
            normalizedCapacity--;
            normalizedCapacity |= normalizedCapacity >>> 1;
            normalizedCapacity |= normalizedCapacity >>> 2;
            normalizedCapacity |= normalizedCapacity >>> 4;
            normalizedCapacity |= normalizedCapacity >>> 8;
            normalizedCapacity |= normalizedCapacity >>> 16;
            normalizedCapacity++;

            if (normalizedCapacity < 0)
            {
                normalizedCapacity >>>= 1;
            }
            assert directMemoryCacheAlignment == 0 || (normalizedCapacity
                    & directMemoryCacheAlignmentMask) == 0;

            return normalizedCapacity;
        }

        if (directMemoryCacheAlignment > 0)
        {
            return alignCapacity(reqCapacity);
        }

        // Quantum-spaced
        if ((reqCapacity & 15) == 0)
        {
            return reqCapacity;
        }

        return (reqCapacity & ~15) + 16;
    }

    int alignCapacity(int reqCapacity)
    {
        int delta = reqCapacity & directMemoryCacheAlignmentMask;
        return delta == 0 ? reqCapacity
                : reqCapacity + directMemoryCacheAlignment - delta;
    }

    void reallocate(PooledByteBuf<T> buf, int newCapacity,
            boolean freeOldMemory)
    {
        if (newCapacity < 0 || newCapacity > buf.maxCapacity())
        {
            throw new IllegalArgumentException("newCapacity: " + newCapacity);
        }

        int oldCapacity = buf.length;
        if (oldCapacity == newCapacity)
        {
            return;
        }

        PoolChunk<T> oldChunk = buf.chunk;
        long oldHandle = buf.handle;
        T oldMemory = buf.memory;
        int oldOffset = buf.offset;
        int oldMaxLength = buf.maxLength;
        int readerIndex = buf.readerIndex();
        int writerIndex = buf.writerIndex();

        allocate(parent.threadCache(), buf, newCapacity);
        if (newCapacity > oldCapacity)
        {
            memoryCopy(oldMemory, oldOffset, buf.memory, buf.offset,
                    oldCapacity);
        }
        else if (newCapacity < oldCapacity)
        {
            if (readerIndex < newCapacity)
            {
                if (writerIndex > newCapacity)
                {
                    writerIndex = newCapacity;
                }
                memoryCopy(oldMemory, oldOffset + readerIndex, buf.memory,
                        buf.offset + readerIndex, writerIndex - readerIndex);
            }
            else
            {
                readerIndex = writerIndex = newCapacity;
            }
        }

        buf.setIndex(readerIndex, writerIndex);

        if (freeOldMemory)
        {
            free(oldChunk, oldHandle, oldMaxLength, buf.cache);
        }
    }

    @Override
    public int numThreadCaches()
    {
        return numThreadCaches.get();
    }

    @Override
    public int numTinySubpages()
    {
        return tinySubpagePools.length;
    }

    @Override
    public int numSmallSubpages()
    {
        return smallSubpagePools.length;
    }

    @Override
    public int numChunkLists()
    {
        return chunkListMetrics.size();
    }

    @Override
    public List<PoolSubpageMetric> tinySubpages()
    {
        return subPageMetricList(tinySubpagePools);
    }

    @Override
    public List<PoolSubpageMetric> smallSubpages()
    {
        return subPageMetricList(smallSubpagePools);
    }

    @Override
    public List<PoolChunkListMetric> chunkLists()
    {
        return chunkListMetrics;
    }

    private static List<PoolSubpageMetric> subPageMetricList(
            PoolSubpage<?>[] pages)
    {
        List<PoolSubpageMetric> metrics = new ArrayList<PoolSubpageMetric>();
        for (PoolSubpage<?> head : pages)
        {
            if (head.next == head)
            {
                continue;
            }
            PoolSubpage<?> s = head.next;
            for (;;)
            {
                metrics.add(s);
                s = s.next;
                if (s == head)
                {
                    break;
                }
            }
        }
        return metrics;
    }

    @Override
    public long numAllocations()
    {
        final long allocsNormal;
        synchronized (this)
        {
            allocsNormal = allocationsNormal;
        }
        return allocationsTiny.value() + allocationsSmall.value() + allocsNormal
                + allocationsHuge.value();
    }

    @Override
    public long numTinyAllocations()
    {
        return allocationsTiny.value();
    }

    @Override
    public long numSmallAllocations()
    {
        return allocationsSmall.value();
    }

    @Override
    public synchronized long numNormalAllocations()
    {
        return allocationsNormal;
    }

    @Override
    public long numDeallocations()
    {
        final long deallocs;
        synchronized (this)
        {
            deallocs = deallocationsTiny + deallocationsSmall
                    + deallocationsNormal;
        }
        return deallocs + deallocationsHuge.value();
    }

    @Override
    public synchronized long numTinyDeallocations()
    {
        return deallocationsTiny;
    }

    @Override
    public synchronized long numSmallDeallocations()
    {
        return deallocationsSmall;
    }

    @Override
    public synchronized long numNormalDeallocations()
    {
        return deallocationsNormal;
    }

    @Override
    public long numHugeAllocations()
    {
        return allocationsHuge.value();
    }

    @Override
    public long numHugeDeallocations()
    {
        return deallocationsHuge.value();
    }

    @Override
    public long numActiveAllocations()
    {
        long val = allocationsTiny.value() + allocationsSmall.value()
                + allocationsHuge.value() - deallocationsHuge.value();
        synchronized (this)
        {
            val += allocationsNormal - (deallocationsTiny + deallocationsSmall
                    + deallocationsNormal);
        }
        return max(val, 0);
    }

    @Override
    public long numActiveTinyAllocations()
    {
        return max(numTinyAllocations() - numTinyDeallocations(), 0);
    }

    @Override
    public long numActiveSmallAllocations()
    {
        return max(numSmallAllocations() - numSmallDeallocations(), 0);
    }

    @Override
    public long numActiveNormalAllocations()
    {
        final long val;
        synchronized (this)
        {
            val = allocationsNormal - deallocationsNormal;
        }
        return max(val, 0);
    }

    @Override
    public long numActiveHugeAllocations()
    {
        return max(numHugeAllocations() - numHugeDeallocations(), 0);
    }

    @Override
    public long numActiveBytes()
    {
        long val = activeBytesHuge.value();
        synchronized (this)
        {
            for (int i = 0; i < chunkListMetrics.size(); i++)
            {
                for (PoolChunkMetric m : chunkListMetrics.get(i))
                {
                    val += m.chunkSize();
                }
            }
        }
        return max(0, val);
    }

    protected abstract PoolChunk<T> newChunk(int pageSize, int maxOrder,
            int pageShifts, int chunkSize);

    protected abstract PoolChunk<T> newUnpooledChunk(int capacity);

    protected abstract PooledByteBuf<T> newByteBuf(int maxCapacity);

    protected abstract void memoryCopy(T src, int srcOffset, T dst,
            int dstOffset, int length);

    protected abstract void destroyChunk(PoolChunk<T> chunk);

    @Override
    public synchronized String toString()
    {
        StringBuilder buf = new StringBuilder().append("Chunk(s) at 0~25%:")
                .append(StringUtil.NEWLINE).append(qInit)
                .append(StringUtil.NEWLINE).append("Chunk(s) at 0~50%:")
                .append(StringUtil.NEWLINE).append(q000)
                .append(StringUtil.NEWLINE).append("Chunk(s) at 25~75%:")
                .append(StringUtil.NEWLINE).append(q025)
                .append(StringUtil.NEWLINE).append("Chunk(s) at 50~100%:")
                .append(StringUtil.NEWLINE).append(q050)
                .append(StringUtil.NEWLINE).append("Chunk(s) at 75~100%:")
                .append(StringUtil.NEWLINE).append(q075)
                .append(StringUtil.NEWLINE).append("Chunk(s) at 100%:")
                .append(StringUtil.NEWLINE).append(q100)
                .append(StringUtil.NEWLINE).append("tiny subpages:");
        appendPoolSubPages(buf, tinySubpagePools);
        buf.append(StringUtil.NEWLINE).append("small subpages:");
        appendPoolSubPages(buf, smallSubpagePools);
        buf.append(StringUtil.NEWLINE);

        return buf.toString();
    }

    private static void appendPoolSubPages(StringBuilder buf,
            PoolSubpage<?>[] subpages)
    {
        for (int i = 0; i < subpages.length; i++)
        {
            PoolSubpage<?> head = subpages[i];
            if (head.next == head)
            {
                continue;
            }

            buf.append(StringUtil.NEWLINE).append(i).append(": ");
            PoolSubpage<?> s = head.next;
            for (;;)
            {
                buf.append(s);
                s = s.next;
                if (s == head)
                {
                    break;
                }
            }
        }
    }

    @Override
    protected final void finalize() throws Throwable
    {
        try
        {
            super.finalize();
        }
        finally
        {
            destroyPoolSubPages(smallSubpagePools);
            destroyPoolSubPages(tinySubpagePools);
            destroyPoolChunkLists(qInit, q000, q025, q050, q075, q100);
        }
    }

    private static void destroyPoolSubPages(PoolSubpage<?>[] pages)
    {
        for (PoolSubpage<?> page : pages)
        {
            page.destroy();
        }
    }

    private void destroyPoolChunkLists(PoolChunkList<T>... chunkLists)
    {
        for (PoolChunkList<T> chunkList : chunkLists)
        {
            chunkList.destroy(this);
        }
    }

    static final class HeapArena extends PoolArena<byte[]>
    {

        HeapArena(PooledByteBufAllocator parent, int pageSize, int maxOrder,
                int pageShifts, int chunkSize, int directMemoryCacheAlignment)
        {
            super(parent, pageSize, maxOrder, pageShifts, chunkSize,
                    directMemoryCacheAlignment);
        }

        @Override
        boolean isDirect()
        {
            return false;
        }

        @Override
        protected PoolChunk<byte[]> newChunk(int pageSize, int maxOrder,
                int pageShifts, int chunkSize)
        {
            return new PoolChunk<byte[]>(this, new byte[chunkSize], pageSize,
                    maxOrder, pageShifts, chunkSize, 0);
        }

        @Override
        protected PoolChunk<byte[]> newUnpooledChunk(int capacity)
        {
            return new PoolChunk<byte[]>(this, new byte[capacity], capacity, 0);
        }

        @Override
        protected void destroyChunk(PoolChunk<byte[]> chunk)
        {
            // Rely on GC.
        }

        @Override
        protected PooledByteBuf<byte[]> newByteBuf(int maxCapacity)
        {
            return HAS_UNSAFE
                    ? PooledUnsafeHeapByteBuf.newUnsafeInstance(maxCapacity)
                    : PooledHeapByteBuf.newInstance(maxCapacity);
        }

        @Override
        protected void memoryCopy(byte[] src, int srcOffset, byte[] dst,
                int dstOffset, int length)
        {
            if (length == 0)
            {
                return;
            }

            System.arraycopy(src, srcOffset, dst, dstOffset, length);
        }
    }

    static final class DirectArena extends PoolArena<ByteBuffer>
    {

        DirectArena(PooledByteBufAllocator parent, int pageSize, int maxOrder,
                int pageShifts, int chunkSize, int directMemoryCacheAlignment)
        {
            super(parent, pageSize, maxOrder, pageShifts, chunkSize,
                    directMemoryCacheAlignment);
        }

        @Override
        boolean isDirect()
        {
            return true;
        }

        private int offsetCacheLine(ByteBuffer memory)
        {
            // We can only calculate the offset if Unsafe is present as
            // otherwise directBufferAddress(...) will
            // throw an NPE.
            return HAS_UNSAFE
                    ? (int) (PlatformDependent.directBufferAddress(memory)
                            & directMemoryCacheAlignmentMask)
                    : 0;
        }

        @Override
        protected PoolChunk<ByteBuffer> newChunk(int pageSize, int maxOrder,
                int pageShifts, int chunkSize)
        {
            if (directMemoryCacheAlignment == 0)
            {
                return new PoolChunk<ByteBuffer>(this,
                        allocateDirect(chunkSize), pageSize, maxOrder,
                        pageShifts, chunkSize, 0);
            }
            final ByteBuffer memory = allocateDirect(
                    chunkSize + directMemoryCacheAlignment);
            return new PoolChunk<ByteBuffer>(this, memory, pageSize, maxOrder,
                    pageShifts, chunkSize, offsetCacheLine(memory));
        }

        @Override
        protected PoolChunk<ByteBuffer> newUnpooledChunk(int capacity)
        {
            if (directMemoryCacheAlignment == 0)
            {
                return new PoolChunk<ByteBuffer>(this, allocateDirect(capacity),
                        capacity, 0);
            }
            final ByteBuffer memory = allocateDirect(
                    capacity + directMemoryCacheAlignment);
            return new PoolChunk<ByteBuffer>(this, memory, capacity,
                    offsetCacheLine(memory));
        }

        private static ByteBuffer allocateDirect(int capacity)
        {
            return PlatformDependent.useDirectBufferNoCleaner()
                    ? PlatformDependent.allocateDirectNoCleaner(capacity)
                    : ByteBuffer.allocateDirect(capacity);
        }

        @Override
        protected void destroyChunk(PoolChunk<ByteBuffer> chunk)
        {
            if (PlatformDependent.useDirectBufferNoCleaner())
            {
                PlatformDependent.freeDirectNoCleaner(chunk.memory);
            }
            else
            {
                PlatformDependent.freeDirectBuffer(chunk.memory);
            }
        }

        @Override
        protected PooledByteBuf<ByteBuffer> newByteBuf(int maxCapacity)
        {
            if (HAS_UNSAFE)
            {
                return PooledUnsafeDirectByteBuf.newInstance(maxCapacity);
            }
            else
            {
                return PooledDirectByteBuf.newInstance(maxCapacity);
            }
        }

        @Override
        protected void memoryCopy(ByteBuffer src, int srcOffset, ByteBuffer dst,
                int dstOffset, int length)
        {
            if (length == 0)
            {
                return;
            }

            if (HAS_UNSAFE)
            {
                PlatformDependent.copyMemory(
                        PlatformDependent.directBufferAddress(src) + srcOffset,
                        PlatformDependent.directBufferAddress(dst) + dstOffset,
                        length);
            }
            else
            {
                // We must duplicate the NIO buffers because they may be
                // accessed by other Netty buffers.
                src = src.duplicate();
                dst = dst.duplicate();
                src.position(srcOffset).limit(srcOffset + length);
                dst.position(dstOffset);
                dst.put(src);
            }
        }
    }
}
